1. Field of the Invention
This invention relates to a press, and more particularly to a die changing apparatus for quickly and accurately mounting and exchanging dies to be mounted on the press.
2. Description of the Prior Art
With the recent increase in variety of products which can be produced by a press work operation or the reduction of life cycle of the products, a variety of products are produced in a small quantity in actual factories. When several sorts of the products are produced in the small quantity by the press work operation, it is required to change dies mounted on the press every time when a different type of the press work is conducted. This increases in the percentage of the mounting or exchanging operation of the die in the overall press work operation, which results in a decrease in the working efficiency of the press. In the production system explained hereinabove, it takes much time in such preparatory press work operations that upper and lower dies are prepared and mounted on the press in exact alignment therewith. Also, when determining the mounting position of these dies, accuracy and skill are required. Accordingly, it has now been an important problem to improve such preparatory operations in view of the reduction of working hours, the simplification of press work operations and the reduction of manufacturing cost.
In order to shorten and simplify the preparatory operations, various die changing apparatuses which are generally referred to as a quick die changing apparatus and make it possible to mount, exchange or alinge the dies on the press for a short period of time have been proposed, and some of the apparatus have been actually put to practical use.
The die changing apparatus of this type generally includes a means for determining mounting position of dies with respect to an upper surface of bolster of the press and a lower surface of the slide, or, when a die set is used, an upper surface of the die holder and a lower surface of the punch holder, and a means for fixing the dies thus determined the mounting positions at that locations. In such die changing apparatus, it is required that the actuating and releasing operations of the apparatus must be simply performed by a single step.
One example of this type of the die changing apparatus is disclosed in the Japanese Patent Publication No. 46-7668 wherein the positioning of dies is performed in such manners that a base plate on which a die is mounted is inserted into a guide hole formed in a vertically movable slider, the slider is actuated in the vertical direction by means of a pneumatic or hydraulic driving means so as to clamp the base plate onto a mounting surface of the base plate, and guide pins projecting from the mounting surface of the base plate are inserted into holes on the base plate.
In the conventional die changing apparatus, it has been a general practice to use such system that the die or the base plate on which the die is mounted is pressed against its mounting surface to be fixed thereto by using a clamp plate vertically movable with respect to the mounting surface by the pneumatic, hydraulic or manual driving means. However, it is too complicated in its mechanism and is high in the manufacturing cost. The die changing apparatus in which the vertical motion of the clamp plate is controlled by the pnuematic or hydraulic cylinder requires a large scale auxiliary apparatus. As a result, the entire apparatus becomes a large-size and the maintenance and inspection are too complicated.
In addition, in the apparatus having guide pins projected on the mounting surface of the base plate as a means for determining the mounting position of the base plate, the pins will be a hindrance for cleaning the mounting surface of the base plate, and if there exists dusts or the like on its surface, it is impossible to obtain a close contact between the base plate and its mounting surface, which results in deterioration in performing precision press work operations. Furthermore, holes or pockets forming operations are required to mount the dies on the base plate of the die changing apparatus. However, when applying the conventional die changing apparatus for machining the base plate, the existence of the chips or dusts remaining on the mounting surface of the base plate become detrimental obstacles for obtaining the base plate of the precision finishing which can be used as a reference for determining the position of the subsequent die change. Therefore, it can not be applicable to the base plate forming apparatus.